So the alert gives undefined values for the width and height. I think the w and h values of the image from the img.onload calculation is not being passed to the values to return, or it may be returning w and h before the onload calculates them:
function getMeta(url){
var w; var h;
var img=new Image;
img.src=url;
img.onload=function(){w=this.width; h=this.height;};
return {w:w,h:h}
}
// "http://snook.ca/files/mootools_83_snookca.png" //1024x678
// "http://shijitht.files.wordpress.com/2010/08/github.png" //128x128
var end = getMeta("http://shijitht.files.wordpress.com/2010/08/github.png");
var w = end.w;
var h = end.h;
alert(w+'width'+h+'height');
How can I have the alert show the correct width and height?
This question is related to
javascript
image
height
width
ES6: Using async/await
you can do below getMeta
function in sequence-like way and you can use it as follows (which is almost identical to code in your question (I add await
keyword and change variable end
to img
, and change var
to let
keyword). You need to run getMeta
by await
only from async
function (run).
function getMeta(url) {
return new Promise((resolve, reject) => {
let img = new Image();
img.onload = () => resolve(img);
img.onerror = () => reject();
img.src = url;
});
}
async function run() {
let img = await getMeta("http://shijitht.files.wordpress.com/2010/08/github.png");
let w = img.width;
let h = img.height;
size.innerText = `width=${w}px, height=${h}px`;
size.appendChild(img);
}
run();
_x000D_
<div id="size" />
_x000D_
Just pass a callback as argument like this:
function getMeta(url, callback) {_x000D_
var img = new Image();_x000D_
img.src = url;_x000D_
img.onload = function() { callback(this.width, this.height); }_x000D_
}_x000D_
getMeta(_x000D_
"http://snook.ca/files/mootools_83_snookca.png",_x000D_
function(width, height) { alert(width + 'px ' + height + 'px') }_x000D_
);
_x000D_
The w
and h
variables in img.onload
function are not in the same scope with those in the getMeta()
function. One way to do it, is as follows:
Fiddle: http://jsfiddle.net/ppanagi/28UES/2/
function getMeta(varA, varB) {
if (typeof varB !== 'undefined') {
alert(varA + ' width ' + varB + ' height');
} else {
var img = new Image();
img.src = varA;
img.onload = getMeta(this.width, this.height);
}
}
getMeta("http://snook.ca/files/mootools_83_snookca.png");
Get image size with jQuery
(depending on which formatting method is more suitable for your preferences):
function getMeta(url){
$('<img/>',{
src: url,
on: {
load: (e) => {
console.log('image size:', $(e.target).width(), $(e.target).height());
},
}
});
}
or
function getMeta(url){
$('<img/>',{
src: url,
}).on({
load: (e) => {
console.log('image size:', $(e.target).width(), $(e.target).height());
},
});
}
Source: Stackoverflow.com